1. Field of the Invention
The present invention relates to an information recording and/or reproducing apparatus for recording information on an optical information recording medium and/or reproducing the information, and more particularly to an optical information recording and/or reproducing apparatus which is suitable for bit edge recording (which is also called pit edge recording).
2. Related Background Art
As information is utilized more extensively, a large capacity information recording and/or reproducing apparatus is required. An optical information recording and/or reproducing apparatus which optically records and/or reproduces information has been attracting notice as one which meets the above requirement. An information recording mode in such an optical information recording and/or reproducing apparatus includes bit position recording (mark interval recording) in which the significance of the information is in the position of the center of the record bit, and bit edge recording (mark length recording) in which the significance of the information is in the position of the bit edge. The bit position recording has a characteristic of exactly recording the information while the bit edge recording has the advantage that its recording density is 1.5 times higher than bit position recording. Accordingly, bit edge recording is advantageous for achieving high density recording and bit edge recording has been actively studied recently.
However, bit edge recording has the following problem. In a so-called heat mode recording in which photo-energy is converted to thermal energy, which is used to record information, edge positions at the beginning and the end of the record bit are determined by a critical temperature at the time of the recording. Accordingly, the edge position of the record bit is easily affected by the surrounding temperature of the apparatus and the internal temperature. FIGS. 1A to 1C show changes in the record bit relative to the variation of temperature. FIG. 1A shows a record bit 40a during low temperature recording, FIG. 1B shows a record bit 40b during ordinary temperature recording, and FIG. 1C shows a record bit 40c during high temperature recording. Recording conditions other than the temperature are identical. The higher the temperature, the larger the area of the record bit and the more the edge position of the record bit changes.